Sulfonated covalent organic frameworks (COFs) incorporated cellulose triacetate/cellulose acetate (CTA/CA)-based mixed matrix membranes for forward osmosis

The comparably low performance hinders the application of CTA based forward osmosis (FO) membranes. Herein, sulfonated-COFs incorporated CTA/CA membranes were designed to enhance the FO performance, taking advantages of the sulfonated COFs with high hydrophilicity, size exclusion and electrostatic repulsion to salt. Two COFs with different pore size were synthesized and sulfonated to prepare hydrophilic COF-SO3H. The COF-SO3H with different loading was then added into CTA/CA casting solution to fabricate incorporated membranes. Characterizations and FO tests revealed that an appropriate amount of COF-SO3H in the membrane matrix could increase membrane porosity, reduce structural parameter (S), bring more negative charges and improve hydrophilicity, leading to enhanced permeability, higher selectivity and suppressed internal concentration polarization. One of the synthesized COF-SO3H, named TATP-SO3H, had a pore size of 0.84 nm, ideal for both easy passthrough of water and high rejection to salt. The XPS results verified the existence of H-bonding between TATP-SO3H and CTA/CA. The membrane with 0.2 wt% TATP-SO3H loading had the best porosity and S, and achieved high flux (13.34 LMH) and selectivity (Jw/Js 6.26 L/g) in FO mode, both of which were 2–3 times of those of the neat CTA/CA membrane and the unfunctionalized-COFs incorporated membrane.